First test effect in intravenous glucose tolerance testing.

Abstract

AIMS:

Intravenous glucose tolerance testing (IVGTT) is a common test of β-cell function in which a glucose load is administered and insulin and/or C-peptide responses are monitored. Since the first IVGTT may be more stressful and stress may alter β-cell secretion or hepatic insulin extraction, we asked whether there was a first test effect.

METHODS:

Insulin and C-peptide responses were compared from two sequential IVGTTs performed within 6 months during staging for the Diabetes Prevention Trial-Type 1 (DPT-1) in 368 people at high risk for type 1 diabetes. Insulin data (1+3 min) were used because the first phase insulin response (and peak insulin concentration) occurs within this time frame. Areas under the curve (AUC) calculations represent early insulin or C-peptide responses from 0 through 10 min post-glucose challenge.

RESULTS:

More than half of all subjects were found to have first test values lower than the second. This was true for all measures of both insulin and C-peptide but the frequency was significantly different only for insulin measures corrected for basal and for insulin AUC (p < 0.05). However, for subjects (n = 99) whose 1+3 min insulin response was <10th percentile on the first test, there was a significant increase on the second test (p < 0.05). The C-peptide: insulin ratio did not change significantly between tests, indicating that differences are due to changes in β-cell secretion rather than hepatic insulin uptake.

CONCLUSIONS:

A statistically significant first test effect occurs during the IVGTT attributable to variations in insulin secretion rather than hepatic uptake.

• Authors: Heba M Ismail, Kama S White, Jeffrey P Krischer, H Peter Chase, David Cuthbertson, Jerry P Palmer, DPT-1 Study Group
• Journal: Pediatric diabetes (Pediatr Diabetes) Vol. 16 Issue 2 Pg. 129-37 (Mar 2015) ISSN: 1399-5448 [Electronic] Denmark
• PMID: 23944770 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)
• Copyright: © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Chemical References

• C-Peptide
• Insulin
• Glucose

Topics

• Adolescent
• Adult
• C-Peptide (blood)
• Child
• Child, Preschool
• Diabetes Mellitus, Type 1 (epidemiology)
• Family Health
• Glucose (administration & dosage, metabolism)
• Glucose Intolerance (blood, complications, diagnosis, metabolism)
• Glucose Tolerance Test
• Humans
• Infusions, Intravenous
• Insulin (blood, metabolism)
• Insulin Secretion
• Insulin-Secreting Cells (metabolism)
• Liver (metabolism)
• Middle Aged
• Reproducibility of Results
• Risk
• Stress, Psychological (complications)
• Young Adult